Exchange of an oxygen lance for liquid steel conversion

ABSTRACT

An oxygen lance assembly includes a lance body which can be coupled and decoupled from a head through the use of a plug and socket junction. The plug part of the junction can be located on the lance body and provided with a plurality of axially spaced cylindrical male sealing surfaces. These are adapted to mate with corresponding female sealing surfaces provided in the head. The sealing surfaces mate with a clearance and the required seal is achieved by mounting O-rings exclusively on each male sealing surface. This provides for convenient inspection of the O-rings. Damage to the O-rings caused by vibration is prevented by cylindrical guide surfaces having a close sliding fit which serve to keep the plug part coaxial in the socket. Alignment of the plug in the socket is achieved by increasing the radius of each cylindrical sealing surface the further it is from the top of the socket via frusto-conical guide surfaces.

The present invention is concerned with the structure and process ofexchange of an oxygen lance for use in the conversion of iron to steel.

In the process for the conversion of pig iron to steel oxygen is blownonto or through the top surface of molten pig iron and scrap containedin a converter vessel. In this specification oxygen is to be taken to beany gas, including air, or mixtures of gases, which might be blown ontothe pig iron/steel mixture unless otherwise stated.

A conventional oxygen lance assembly consists of a lance body coupled toa head. The lance body is comprised of at least an inner pipe,intermediate pipe and an outer pipe arranged concentrically. The innerpipe provides an oxygen passage to deliver oxygen from the normallyupper head end to a lower tip end from which it is expelled. The annularspaces between the pipes provide a water passage whereby water coolantis pumped from the head to the tip and returned to the head. The headprovides means to couple the lance body to oxygen and water supplies.The lance body has to be changed frequently because it deterioratesrapidly in the hostile working environment and for process reasons.

A conventional lance assembly is known from U.S. Pat. No. 3,170,977.U.S. Pat. No. 3,170,977 illustrates a lance assembly known as a plug andsocket system. In this assembly the lance body has a head end in theform of a plug which plugs into a head in the form of a socket. In usethe head is permanently supported on a gantry. Various pipes areconnected to ports in the head whereby oxygen and coolant fluids can bedelivered to and circulated in the lance. The head end of the innermostpipe projects from the head end of the intermediate pipe which in turnprojects from the head end of the outer pipe. Thus cylindricalperipheral male mating surfaces are exposed on each pipe. Within thesocket of the head, cylindrical female peripheral mating surfaces areprovided which engage with the exposed male mating surfaces of eachpipe. Thus, when the lance body is plugged into the head socket axiallyspaced annular chambers are formed which communicate with water deliveryand return ports in the head and with the corresponding passages in thelance body. The inner pipe sockets directly into an inner pipe aperturecommunicating with the oxygen delivery port in the head. To preventwater leaks into the oxygen passage a pair of O-ring seals are retainedin annular channels formed the female mating surface which receives theinner pipe mating surface.

The lance head is coupled to the lance body by means of hooks formed onone of the lance head and body which engage with pins formed on theother of the lance head and body. To exchange a lance body, the lancebody is first engaged and suspended by means of a crane. The pins arereleased from the hooks and the old lance body displaced axially towithdraw the head end from the socket in the head and is then carriedaway. A replacement lance body is carried in by a crane. The head end ofthe replacement lance body must then be accurately aligned coaxially sothat the sealing surfaces, which have sliding fit tolerances, can beslid into engagement by having the crane raise the lance body. The hooksare then engaged with the pins to retain the lance body in the head andthe crane is withdrawn.

The lance body and head are heavy and the lance body has a large momentof inertia. The lance body is suspended from a crane via a hook andtrunnion pin arrangement. The crane operator is also necessarily remotefrom the head and must be guided by an assistant on a gantry supportingthe head, it is consequently difficult to accurately align the head andlance body.

The aforementioned problems experienced with aligning the conventionallance body and head must be obviated in order to automate the exchangeof the lance body.

Because there is a close sliding fit tolerance between the matingsurfaces, the mating surfaces are subject to wear from abrasion and thisencourages corrosion so reducing the endurance of the lance body and thehead.

Because the respective mating surfaces of the head and lance body mustpass over each other as the lance body is introduced to the head, thereis a serious risk of the O-rings being damaged. Because the O-rings areretained in the head socket they are difficult to inspect and maintain.

In order to alleviate the technical problems exhibited by theaforementioned prior art there is provided an oxygen lance assemblycomprising:

a head and

a lance body,

a plug part being formed on one of the lance body or the head,

a socket being formed in the other of the lance body or the head toreceive the plug part and so form a plug and socket junction,

the plug part having a plurality of cylindrical peripherally extendingaxially spaced exclusively male mating surfaces and,

the socket having a plurality of cylindrical peripherally extendingexclusively female mating surfaces spaced axially to cooperate one eachwith each male mating surface to separate passages for the transport ofoxygen or coolant through the plug and socket junction,

at least one annular sealing element mounted to engage betweencooperating male and female mating surfaces, characterised in that,

the sealing element is mounted to be retained on the male mating surfaceof the plug.

Preferably the socket is formed in the head and the plug part on thelance body.

Preferably conic guide surfaces are provided radially spaced from themating surfaces arranged to progressively correct any misalignment ofthe mating surfaces before the mating surfaces engage duringinstallation of the plug part in the socket. The guide surfaces may alsocomprise cylindrical surfaces. The cooperating cylindrical guidesurfaces on the plug part and the socket may have a sliding fittolerance and cooperating mating surfaces on the socket and the plugpart may have a clearance so that cooperating mating surfaces do nottouch. A virtue of this is that wear on the O-rings and mating surfacesis reduced.

Preferably at least one cylindrical guide surface on the plug part isdisposed to engage with the cooperating cylindrical guide surface in thesocket before the mating surfaces on the socket and plug part engage.This ensures that the male and female mating surfaces are accuratelyaligned during installation.

Because there is little or no wear on the mating surfaces it may beworthwhile that at least some of the mating surfaces are coated toresist corrosion. Also components of the head which come in contact withwater may be made from costly but corrosion resistant materials such asstainless steel because the abrasive wear to which the prior artassembly is subject is alleviated. Thus it may be economic to make askirt of the head from stainless steel because the skirt provides thefemale mating surfaces exposed to water.

Preferably the sealing elements are O-ring seals retained in annulargrooves. However, lip seals or other elastomer seals having appropriatemountings could be used.

To minimise abrasion it is preferable that the radius of each matingsurface is greater than that of any mating surface closer to the socketend of the plug part.

According to a second aspect of the invention an oxygen lance assemblycomprises:

a head and

a lance body,

a plug part formed on one of the head or lance body,

a socket formed in the other of the head or lance body to receive theplug part and so form a plug and socket junction,

the plug part having male mating surfaces provided by a plurality ofcylindrical peripherally extending axially spaced surfaces and,

the socket having a plurality of cylindrical peripherally extendingfemale mating surfaces spaced axially to cooperate one each with eachmale mating surface to isolate passages for the transport of oxygen orcoolant through the plug and socket junction,

characterised by the provision of guide surfaces on at least one of thesocket or plug part whereby the plug part and the socket are accuratelyaligned before the mating surfaces overlap.

According to a third aspect of the present invention a lance bodyexchange system comprises a lance assembly having a lance head, anexchangeable lance body, and a support structure, said lance body havinga suspension means adapted for cooperation with said support structurewhereby the lance body can be statically suspended while the lance headis displaced vertically to effect the connection and/or disconnection ofthe lance head from the lance body.

Preferably the support structure comprises vertically extending guidechannels and a retractable support arm capable of engaging suspensionmeans provided on the lance body.

The head may be supported on a vertically displaceable carriage mountedon the support structure.

A clamping arm may be extensible mounted on the carriage to engagesuspension means remote from the head on the lance body so that thelance body can be clamped to the head and the carriage for use.

It will be appreciated that in this aspect of the invention theimprovement lies in not having to provide a crane to vertically displaceor hold the lance body for presentation of mating faces on the lancebody with mating faces on the lance head in order to effect a junctionof the lance head and body. Also, the lance body is clamped into thehead by the clamping arm at a position remote from the head. Thisprovides good control of the lance during use by helping to dampvibrations caused by the violent turbulent flow of the fluids.

According to a fourth aspect of the present invention there is provideda process of exchanging an oxygen lance body attached to a lance headcomprising the steps of:

statically supporting the lance body,

unclamping the junction of the lance body and the lance head and liftingthe lance head away from the lance body,

statically suspending a replacement lance body,

lowering the lance head onto the replacement lance body so that theweight of the lance head forces mating surfaces of the lance headtogether with the mating surfaces of the lance body,

clamping the lance head to the lance body ready for use.

The process preferably comprises the step of statically supporting theused and/or replacement lance body by means other than a crane duringattachment or detachment of the lance head.

An oxygen lance assembly, a system for exchanging a lance body of anoxygen lance assembly, and a process of exchanging an oxygen lance bodyattached to an oxygen lance head, embodying the present inventions willnow be described, by way of example only, with reference to theaccompanying illustrative drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned view of a first embodiment of the oxygenlance assembly,

FIG. 2 is an axially split section view of a second embodiment of thelance assembly,

FIG. 3 is an axially split section view of a third embodiment of thelance assembly,

FIG. 4 is an axially split section view of a fourth embodiment of thelance assembly,

FIG. 5 is an axially split multiple section of a plug and socket headassembly with the plug partially received into the socket on the lefthand side and the plug fully received into the socket on the right handside.

FIGS. 6a, 6b and 6c illustrate an apparatus and method for lance bodyexchange.

In the embodiment shown in FIG. 1, a lance head is generally indicatedby the arrow 1 while a lance body is indicated by the arrow 2. The lancehead I is assembled from an annular flange 10, which is preferably madeof a non-ferrous inert material such as bronze. An oxygen supply hose 11is bolted on to the flange 10 to deliver oxygen through the aperture inthe flange 10. An elongate skirt 12 made of steel is secured by bolts todepend from the flange 10. Ports (not shown) for the input and output ofcoolant water are provided, vertically spaced, in the skirt 12. Theinterior surface of the skirt is substantially vertical but providedwith two cylindrical vertically spaced female mating surfaces 13 and 14which stand proud of the nominal interior surface. A third matingsurface 15 is formed by a shoulder portion of the flange which dependsinside the skirt 12. The surfaces inside the head form a socket.

The lance body is assembled from an inner oxygen pipe 3, an intermediatesurrounding pipe 4 and an outer pipe 5. The pipe 3 provides a passagefor oxygen to pass to a tip of the lance assembly. The annular spacebetween the intermediate pipe 4 and the inner pipe 3 provides a coolantdelivery passage 16 for transport of coolant water from the head end ofthe lance body towards the tip. An annular passage between theintermediate pipe and the outer pipe provides a coolant return passage17.

At the head end of the oxygen pipe 3 the oxygen passage communicateswith an open aperture 18. The coolant delivery passage 16 communicateswith an annular coolant delivery chamber 19 formed in a manifold. Themanifold also provides an annular coolant return chamber 20 whichcommunicates with the coolant return passage 17. The coolant returnchamber 20 is located beneath the coolant delivery chamber 19 andsurrounds a portion of the coolant delivery pipe 4. A first ring ofcoolant delivery ports 21 is provided in the wall of the manifold partdefining the coolant delivery chamber 19. A second ring of coolantreturn ports 22 is formed in the wall of the manifold part defining thecoolant return chamber 20.

A first male cylindrical mating surface 23 is provided on a raised ridgeextending around the outside of the manifold immediately above thecoolant delivery ports 21. A second cylindrical male mating surface 24is provided on a raised ridge extending around the manifold between thefirst ring of ports 21 and the coolant discharge ports 22. A thirdcylindrical male mating surface 25 is provided on a raised ridgeextending around the manifold immediately beneath the coolant dischargeports 22. Each of the mating surfaces 23,24,25 is provided with anO-ring seal located in an annular groove.

In use the lance body 2 is statically supported. The lance head 1 islifted onto the manifold and the weight of the lance head assists inpushing the lance head 1 onto the manifold as shown in FIG. 1. In thiscondition the mating surfaces 23,24,25 and the O-ring seals of themanifold mate with the mating surfaces 13,14,15 of the head to form anoxygen delivery chamber, a coolant delivery chamber and a coolant returnchamber. The oxygen delivery chamber is formed at the top of the headfor the delivery of oxygen through the aperture 18 to the oxygen passagein the pipe 3. A coolant delivery chamber is formed between the matingsurfaces 23,15 and 24, 14 and provides for the delivery of coolant fromthe coolant delivery port in the skirt 12 through the coolant deliveryports 21. The third chamber is formed between the mating surfaces 14, 24and 13,25 and provides for the passage of return coolant from the ports22 to a water return port in the skirt 12.

The weight of the lance head 1 holds it in place while it is beingclamped to the lance body 2. The assembled lance is then ready for use.

After use the exhausted lance body is removed by the reverse of theinstallation procedure.

Referring to the second embodiment of the invention illustrated in FIG.2, components corresponding to those of the first embodiment aredesignated by the same numerals. The lance head 1 differs from that ofthe previous embodiment in that the annular flange 10 and the skirt 12are a unitary structure of steel. An annular insert 28 of an inertmaterial such as bronze is received into the aperture in the flange 10.The insert has a socket 29 machined into its underside to provide amating surface 15 and to receive a complimentarily shaped hollow plug 30formed onto the end of the oxygen pipe 3 with a cooperating matingsurface 23. An O-ring seal is located in the mating surface 23. Themating surfaces 15 and 23 taper to guide the plug and socket centrally.

The head end of the intermediate pipe 4 is spaced downwardly from theplug 30 and provided with a radially extending flange 31 which providesthe mating surface 24. An O-ring seal is provided in a groove in theradially outer surface of the flange 31 which seals against the innersurface of the skirt. A leading edge of the flange 31 is provided with atapering guide surface 32. The flange 32 extends radially out from theplug 30 and so tends to centre the plug as the lance head 1 is lowered.A water delivery chamber is thus formed between the annular flange 10,the plug 30, skirt 12 and oxygen pipe 3 and coolant passes through thecoolant delivery port in the skirt (not shown) into the chamber and fromthe chamber directly into the annular delivery passage 16.

The end of the outer pipe 5 is secured spaced down from the flange 31and provided with a flange 33 which provides a mating surface 25 whichmates with the inner surface of the skirt 12. The inner surface of theskirt 12 is of uniform radius. An O-ring seal is located in a groove inthe mating surface 25. Thus a coolant return chamber is formed betweenthe flange 33, intermediate pipe 4, flange 32 and skirt 12. Coolant isreturned to the chamber directly from the return passage 17 and passesfrom the chamber through a coolant return port (not shown) formed in theskirt. A tapered guide surface 34 is provided on the leading edge of theflange 33.

The second embodiment of the lance assembly does not require a complexmanifold formation on the head end of the lance body. Further theprovision of raised mating surfaces on the inside of the skirt isobviated simplifying production. Because the flanges 31 and 33 extendradially outwards from the plug 30, the plug is accurately centred bythe time the socket 29 is lowered on to it thus reducing the risk ofdamage to the mating faces 15, 23 and ensuring a good seal between thecoolant delivery chamber and the oxygen passage.

The third embodiment illustrated by FIG. 3 is generally similar to thesecond embodiment but differs in that the inner surface of the skirt hasa stepped taper and the flange 34 extends radially outwards from theflange 31. This means that less precision is required in initiallylocating the lance head 1 over the end of the lance body since thetapered guide surfaces 35 formed inside the skirt act to centre thelance body 2.

The process of inserting and separating a lance body in the lance headis the same in the case of each embodiment.

In some applications it is desirable to have additional passages for thedelivery of gases such as oxygen or other gases to a secondary nozzle atthe tip of the lance body where the gases are used for post combustionof the steel making gases. Additional passages for these purposes havepreviously been provided by means of inlet ports further down the lancebody. The fourth embodiment of the invention shown in FIG. 4 provides anadditional oxygen pipe 3' between the inner oxygen pipe 3 and theintermediate pipe 4. A flange 30' of bronze is formed onto the end ofthe pipe 3' to provide a mating surface for cooperation with a matingsurface formed in the skirt 12. An additional oxygen chamber 30a is thusformed between the plug 30, the oxygen pipe 3 and the skirt 12. Anadditional oxygen delivery port 30b is formed in the side of the skirt.

In the fourth embodiment the flange 10 and an upper portion of the skirt12 are formed from inert material such as bronze so that steel fromwhich the rest of the lance body is formed does not come into contactwith the oxygen.

FIG. 5 illustrates a fifth embodiment of the invention and shows thehead 1 and the top end part of the lance body 2. In the fifth embodimentthe mating surfaces are provided by sealing surfaces which do not touch.

The head 1 is formed from a hollow cylinder 40 and a skirt 41 whichdepends from the cylinder 40. An oxygen port 42 is provided on the axisthrough the top of the cylinder 40 so that in use an oxygen deliveryhose 11 can be coupled to the head 1. A post burn oxygen delivery port43 is formed through a side wall of the cylinder 40 to which a post burnoxygen delivery hose can be coupled. It may be noted that the post burnoxygen delivery port may be omitted in some embodiments of theinvention. A coolant water delivery port 44 is formed through the skirtso that a coolant water delivery hose can be coupled to the head 1 todeliver water to the head. A water return port 44' is formed lower inthe head to which a return hose can be coupled for the recovery of hotwater after circulation through the lance assembly.

A socket is formed within the head by means of axially spacedcylindrical peripherally extending sealing surfaces and means definingguide surfaces adapted to accurately align the sealing surfaces duringinsertion of the plug part in the socket before cooperating pairs of thesealing surfaces overlap. The guide surfaces include surfaces which maybe continuous or discontinuous around the periphery of the socket andextend parallel to the axis and surfaces which are inclined to the axisto steer the plug and socket to a coaxial condition. The parallelextending surfaces are preferably cylindrical surfaces and the inclinedsurfaces are preferably conical or frusto-conic.

In particular, working axially away from a socket end adjacent theoxygen port 42, towards a tip end (i.e., towards the tip of the lance)there is a first female sealing surface 45a, this extends to a firstfrusto-conic guide surface 46a having a radius which increases towardsthe tip end. First frusto-conic guide surface 46a extends to a secondfemale sealing surface 45b. The second sealing surface 45b extends to asecond frusto-conic guide surface 46b. Guide surface 46b extends axiallyand radially outwards to a first female cylindrical guide surface 47a.The first cylindrical guide surface 47a is provided on the tip most endof the cylinder 40 and ends at a shoulder which forms part of thejunction with the skirt 41. A cylindrical surface of the skirt 41provides a third sealing surface 45c. The sealing surface 45c extends toa shoulder which extends radially out to a second cylindrical guidesurface 47b. The second cylindrical guide surface 47b extends axially toa third frusto-conic guide surface 46c. The third frusto conic guidesurface 46c extends radially out to a fourth sealing surface 45d whichends at a fourth frusto conic guide surface 46d.

The lance body comprises an inner oxygen pipe 3, an outer oxygen pipe3', an inner water pipe 4 and an outer water pipe 5 each spacedconcentrically about a lance body axis. The inner oxygen pipe 3 providesa passage for oxygen to be delivered to the lance tip from the oxygenport 42. An annular oxygen delivery passage between the inner and outeroxygen pipes 3,3' is for the delivery of post burn oxygen. The annularwater delivery passage formed between the outer oxygen pipe 3' and theinner water pipe 4 is for the delivery of coolant water and a waterreturn passage between the inner and outer water pipes 4,5 is for thereturn of the coolant water.

The head end of the lance body 2 remote from the tip is capped with amanifold plug assembly into which relatively projecting ends of thepipes 3,3',4,5 are received. The plug assembly provides a plug part ofthe lance body 2 adapted for reception in the socket to form a plug andsocket junction. In particular various male sealing surfaces and bothcylindrical and frusto-conic guide surfaces are provided for cooperationwith the female sealing surfaces and guide surfaces of the socket. Theplug assembly is comprised of a top end part which engages the inner andouter oxygen pipes 3,3' and a bottom end part. An oxygen reception porton the axis of the plug assembly communicates with the oxygen passage inthe inner oxygen pipe 3. A first male cylindrical sealing surface 48aextends from the top end of the plug assembly towards the bottom and isdimensioned to provide a clearance fit in the female sealing surface45a. An annular groove is cut into the first male sealing surface 48a toretain a first O-ring 49a which engages between the male and femalesealing surfaces to provide a sealing element. The first O-ring isolatesthe oxygen supply from the post burn supply when the plug assembly isfully installed in the socket.

Towards the bottom, and axially coincident with the post burn oxygenport 43, apertures 50 are provided through the first male sealingsurface 48a to communicate with the post burn oxygen passage.

The first male sealing surface 48a extends to a first male frusto-conicguide surface 51a which extends radially out to a second malecylindrical sealing surface 48b. The second male cylindrical sealingsurface 48b has a radius to form a clearance fit in the second femalecylindrical sealing surface 45b. An annular groove is cut into thesecond male sealing surface to retain a second O-ring 49b which providesa sealing element to act between the second sealing surfaces 45b and48b.

The second male sealing surface 48b extends to a second frusto-conicguide surface 51b. Second frusto-conic guide surface 51b extendsradially out to a first male cylindrical guide surface 52a. The firstmale cylindrical guide surface 52a has a radius to provide a closesliding fit in the first female cylindrical guide surface 47a.

The first male cylindrical guide surface 52a extends to an annularchannel 53 disposed to cooperate with the water delivery port 44. Theannular channel 53 communicates with the water delivery passage viaholes 54 bored parallel to the axis. The annular channel 53 extends to aflange, which extends radially out and by means of which the socket endpart of the plug assembly is bolted to a tip end part.

A third frusto-conic guide surface 51c is formed on the tip end part ofthe plug assembly immediately adjacent the flange. The thirdfrusto-conic guide surface 51c extends to a third male sealing surface48c. The third male sealing surface 48c has a radius to form a clearancefit with the third female sealing surface 45c. A sealing element isprovided by a third O-ring 48c retained in an annular groove formed inthe third male sealing surface 48c. The third male sealing surfaceextends to a fourth male frusto-conical guide surface 51d which extendsto a second male cylindrical guide surface 52b. The second cylindricalguide surface 52b has a radius to form a close sliding fit with thesecond female cylindrical guide surface.

A ring of apertures 54 are formed in an annular channel 55 extendingaround the second cylindrical guide surface 52b. The apertures 54 andthe channel communicate with the water return port 44' and the waterreturn passage.

The annular channel 55 extends to a fifth frusto conical guide surface51e. The fifth frusto conical guide surface extends to a fourth malesealing surface 48d which forms a clearance fit with the fourth femalesealing surface 45d.

The fourth male sealing surface 48d is provided with an O-ring seal 49dretained in an annular groove for sealing engagement between the sealingsurfaces 45d and 48d.

It will be realised that the provision of frusto-conic guide surface oneach of the head and the plug part ensures that the plug part is steeredonto the axis of the head as it is inserted so that the head and plugmay be considerably out of alignment prior to insertion of the plug andyet the lance body can still be reliably coupled with the head.

The axial separation of the cylindrical guide surfaces is arranged sothat the second cylindrical guide surfaces 47b and 52b are engagedbefore any of the cooperating sealing surfaces are axially coincident.Consequently there is no risk of the sealing surfaces abrading eachother or damaging the O-rings 49.

Because there is no problem with abrasion of the sealing surfaces thesealing surfaces 45 and 48 have anti-corrosion coatings such as bronzeplasma coating.

The radial separation of all the cylindrical surfaces, particularly thesealing surfaces, ensures that there is contact only between an O-ring16 and the sealing surface against which it is meant to seal. Thisminimises wear on the O-rings 16 and maximises reliability.

FIGS. 6a to 6c illustrate a preferred carriage and clamping apparatuswhereby a lance body 2 can be exchanged in a lance head 1.

FIG. 6a shows the replacement lance body 2 suspended from a crane 60 bymeans of upper trunnions 61 projecting from the sides of the lance body2. The lance body 2 is steered into a position between a pair ofopposing vertical channel section guides 62 which have passages (notshown) formed in the sides through which the upper trunnions 61 pass.Middle trunnions 63 and lower trunnions 64 are also provided on thelance body 2. These also pass through passages (not shown) provided inthe guides 62.

A temporary support arm 65 is pivotally mounted on a gantry and ispivoted into a horizontal position by means of a ram. The end of the armis provided with notches into which the lower trunnions 64 seat whenlowered by the crane 60. The lance body 2 is now securely supported bythe support arm 65 and the channels 62 and the crane 60 can be removed.

The head 1 is carried on a vertically displaceable carriage 66, as is aclamping arm 67. While the lance body 2 is brought in by the crane 60the carriage 66 is at a raised position as shown in FIG. 6a. Once thelance body 2 is supported on the support arm the carriage 66 is loweredas shown in FIG. 6b so that the head 1 is lowered onto the lance body 2.

The head 1 and lance body 2 are supported on the carriage to permit somerelative lateral and pivotal movement between them so that in theprocess of lowering the carriage 66 the head 1 is guided by means of thepreviously described guide surfaces onto the plug end of the lance body2 to form the plug and socket junction.

The clamping arm 67 is telescopically mounted on the carriage 66 andspring biased to the extended position shown in FIGS. 6a and 6c. A ramis provided to retract the clamping arm 67 as shown in FIG. 6b as thecarriage is lowered so that a claw 68 on the end of the clamping arm 67can pass around the middle trunnions 63. The clamping arm is thenextended so that the middle trunnions 63 seat on to the claw 68. Thesupport arm 65 is now retracted as shown in FIG. 6c and the lance head 1and lance body 2 are clamped together and can be raised and lowered bythe carriage 66 ready for use.

The process of installing the lance body 2 is reversed to remove thelance body 2.

What is claimed is:
 1. An oxygen lance assembly comprising:a head and alance body, a plug part being formed on the lance body, a socket beingformed in the head to receive the plug part and so form a plug andsocket junction whereby the lance body and the plug part can quickly beexchanged, as a unit, by plugging and unplugging the plug part in thesocket, sealing surfaces of the plug part being provided exclusively bya plurality of cylindrical peripherally extending axially spaced malemating surfaces and, sealing surfaces of the socket being providedexclusively by a plurality of cylindrical peripherally extending femalemating surfaces spaced axially to cooperate one each with each malemating surface to separate passages for the transport of oxygen orcoolant through the plug and socket junction, wherein annular sealingelements are mounted to be retained one each on each male mating surfaceof the plug to engage between cooperating male and female matingsurfaces, whereby the plug and socket junction is tolerant ofdisplacement and misalignment in the axial direction.
 2. An assemblyaccording to claim 1 further comprising guide surfaces radially spacedfrom the mating surfaces arranged to progressively correct anymisalignment of the mating surfaces before the mating surfaces engageduring installation of the plug part in the socket.
 3. An assemblyaccording to claim 2 wherein the guide surfaces comprise frusto-conicsurfaces.
 4. An assembly according to claim 2 wherein cooperating guidesurfaces on the plug part and the socket have a sliding fit toleranceand the mating surfaces provided by the cooperating sealing surfaces onthe socket and the plug part have a clearance fit.
 5. An assemblyaccording to claim 3 wherein at least one guide surface on the plug partis disposed to engage with the cooperating guide surface in the socketbefore the sealing surface on the socket and plug part engage.
 6. Anassembly according to claim 1 wherein at least some of the sealingsurfaces are coated to resist corrosion.
 7. An assembly according toclaim 1 wherein a part of the socket on which are formed the sealingsurfaces is made from a skirt of stainless steel.
 8. An assemblyaccording to claim 1 wherein the sealing elements are O-ring sealsretained in annular grooves.
 9. An assembly according to claim 1 whereinthe radius of each mating surface is greater than that of any matingsurface relatively towards the interior of the socket.
 10. An oxygenlance assembly comprising:a head and a lance body, a plug part beingformed on one of the head and lance body, a socket being formed in theother of the head and lance body to receive the plug part and so form aplug and socket junction whereby the lance body and the plug part canquickly be exchanged, as a unit, by plugging and unplugging the plugpart in the socket, the plug part having male mating surfaces providedby a plurality of cylindrical peripherally extending axially spacedsurfaces and, the socket having a plurality of cylindrical peripherallyextending female mating surfaces spaced axially to cooperate one eachwith each male mating surface to separate passages for the transport ofoxygen or coolant through the plug and socket junction, wherein themating surfaces are provided by sealing surfaces dimensioned so thatcooperating male and female mating surfaces mate with a clearance, andwherein male guide surfaces are provided on the plug to engagecorresponding female guide surfaces provided in the socket which act toalign the male and female mating surfaces before they mate and maintainthe clearance of the male and female mating surfaces after they mate.11. An oxygen lance assembly according to claim 10 wherein each of themating surfaces has a radius greater than that of every mating surfacerelatively towards the interior of the socket.
 12. An oxygen lanceassembly according to claim 10 further comprising a guide surfaceinclined towards the axis to coaxially center the plug part on insertionto the socket.
 13. An oxygen lance assembly according to claim 11wherein the inclined guide surface is a frusto-conic guide surface. 14.An oxygen lance assembly according to claim 10 further comprisingcooperating male and female guide surfaces extending parallel to theaxis to maintain the clearance between the mating surfaces.
 15. Anoxygen lance assembly according to claim 14 wherein the parallelextending guide surface is provided by a cylindrical guide surface. 16.An oxygen lance assembly according to claim 1 in combination with alance body exchange system comprising a support structure, the lancebody having a suspension means adapted for cooperation with the supportstructure whereby the lance body can be statically suspended while thelance head is displaced vertically, the suspension means permittingrelative motion between the lance head and the lance body in a directionperpendicular to the axis to accommodate radial misalignment of thelance head and lance body to effect the connection and disconnection ofthe lance head and the lance body.
 17. A system according to claim 16wherein the support structure comprises vertically extending guidechannels and a retractable support arm capable of engaging suspensionmeans provided on the lance body.
 18. A system according to claim 16wherein the head is supported on a vertically displaceable carriagemounted on the support structure.
 19. A system according to claim 16wherein a clamping arm is extensibly mounted on the carriage to engagesuspension means remote from the head on the lance body so that thelance body can be clamped to the head and the carriage for use.
 20. Aprocess of operating a lance body exchange system according to claim 16comprising the steps of:statically supporting the lance body, unclampingthe junction of the lance body and the lance head and lifting the lancehead away from the lance body, statically suspending a replacement lancebody, lowering the lance head onto the replacement lance body so thatthe weight of the lance head forces sealing surfaces of the lance headtogether with the sealing surfaces of the lance body, clamping the lancehead to the lance body ready for use.
 21. An oxygen lance assemblyaccording to claim 10 in combination with a lance body exchange systemcomprising a support structure, the lance body having a suspension meansadapted for cooperation with the support structure whereby the lancebody can be statically suspended while the lance head is displacedvertically, the suspension means permitting relative motion between thelance head and the lance body in a direction perpendicular to the axisto accommodate radial misalignment of the lance head and lance body toeffect the connection and disconnection of the lance head and the lancebody.
 22. A system according to claim 10 wherein the support structurecomprises vertically extending guide channels and a retractable supportarm capable of engaging suspension means provided on the lance body. 23.A system according to claim 10 wherein the head is supported on avertically displaceable carriage mounted on the support structure.
 24. Asystem according to claim 10 wherein a clamping arm is extensiblymounted on the carriage to engage suspension means remote from the headon the lance body so that the lance body can be clamped to the head andthe carriage for use.
 25. A process of operating a lance body exchangesystem according to claim 10 comprising the steps of:staticallysupporting the lance body, unclamping the junction of the lance body andthe lance head and lifting the lance head away from the lance body,statically suspending a replacement lance body, lowering the lance headonto the replacement lance body so that the weight of the lance headforces sealing surfaces of the lance head together with the sealingsurfaces of the lance body, clamping the lance head to the lance bodyready for use.